Aliyun CentOS server Add swap space

I am now using the Aliyun minimum configured server, 1 cores, 512MB memory, viewing memory information swap space is 0MB, as follows:
[root@www ~]# free-m
              total       used        free     shared    buffers     Cached
mem:           494         124        370           0          7        
-/+ buffers/cache:         74         419
swap:            0           0          0

After searching for information, the following solutions are available in the Aliyun forum:

Source Address: http://bbs.aliyun.com/read/139905.html?spm=5176.7189909.0.0.bE6Z3x

1. Access to catalogue

cd/var/

2. Get the block of swap files to add (here in 1GB for example, Count = 1024 x 1024)

DD If=/dev/zero of=swapfile bs=1024 count=1048576

3. Create a swap file

/sbin/mkswap Swapfile

4. Activate swap file

/sbin/swapon Swapfile (now you can see the swap space with the free command)

5. See if swap information is correct

/sbin/swapon–s

6. Add to Fstab file to allow system to boot automatically when booting

echo "/var/swapfile swap defaults 0 0" >>/etc/fstab

7. Modify/etc/rc.local

Cat/etc/rc.local
Touch/var/lock/subsys/local
#swapoff-A

8. Reboot the server

Reboot

The results are as follows: